Lithium silylamides

Lithium silylamides react smoothly with tiifluoronitrosomethane to give diazenes Traces ot water initiate the decomposition of the latter with liberation of a trifluoromethyl carbanion, which is trapped by carbonyl compounds [775] (equation 116) Desilylation of trialkyl(trifluoromethyl)silanes by fluoride ion produces also a trifluoromethyl carbanion, which adds to carbonyl carbon atoms [136, 137] (equations 117 and 118)... 

V,7V-Diethylcarbamoyl trimethylsilane has been prepared by the reaction of bis(trimethylsilyl) sulphide with bis(A,A-diethylcarbamoyl) mercury (Scheme 30)16. Silylation of the carbamoyl cuprate reagent derived from a lithium amide, by addition of copper(I) cyanide and subsequent exposure to carbon monoxide (1 atm), is also effective75,110. Poor to moderate yields of carbamoyl silanes may be isolated by treatment of lithium silylamides with carbon monoxide and methyl iodide, in a reaction sequence involving a nitrogen to carbon silyl shift in an intramolecular silylation (Scheme 31)111. 

Silylamido groups are used throughout the periodic table to stabilize unusual types of bonding, coordination numbers and oxidation states. Lithium silylamides, generally prepared by reaction of the silylamine with alkyl- or aryllithium derivatives, play an important role in the synthesis of such molecules. 

Lithium silylamides are solids with definite melting points and they may often be distilled in vacuo without decomposition. They are stable in air, but are sensitive against moisture. They decompose explosively when heated with oxygen or treated with concentrated nitric acid. Further reactions of silylamides can be found in reviews 1 2,8. 

In polar solvents lithium silylamides dissolve as coordinated monomers, but by using 12-crown-4 a separation of the lithium cation and the nitrogen-substituted anion can be obtained. In nonpolar solvents the lithium silylamides dissolve as dimers, trimers or oligomers. 

Carbamoyl silanes 100 could be prepared by reaction of lithium silylamides 97 with CO at room temperature and under pressure (30 atm) followed by reaction with methyl iodide (Scheme 25)101. The intermediate carbamoyllithium 98 suffers a rearrangement of the silyl group to afford a new lithium (silylcarbonyl)amide 99, which is finally methylated. 

We were easily able to synthesize the corresponding symmetrical bis(silyl)aminoboranes by reaction of lithium silylamide with dimethyl sulfide-boron dichloride in convenient one-pot reactions (Scheme 3). The lithium amide was formed by adding n-butyllithium to a stirred solution of silylamine in -hexane, followed by the controlled addition of the dimethyl sulfide-boron... 

For example, [LiMg N(SiMe3)2 3] was obtained by the simple addition of LiN-(SiMe3 )2 to Mg N(SiMe3)2 2- It features a magnesium bound to three silylamides in a near-planar fashion (Mg N bond lengths are between 1.998(4) and 2.125(4) A). The lithium ion... 

In contrast to the ammonolysis of chlorosilanes, the four-membered ring was formed along with the six- and eight-membered rings by heating lithium fluoro-silylamide (Scheme 4).16... 

Bis(trimethylsilyl)methylene-bridged bis(lithium difluoro silylamide), preparation, 3, 112 1-15 Bis(trimethylstannyl)calcium, preparation, 3, 859 Bis(triorganosilyl) diazene, preparation, 3, 445 Bis(triorganosilyl)silyl dianions, reactions, 3, 422... 

Cyanofuran-2-[l,2,3,5-diselenadiazolyl] 30 was prepared similarly (Scheme 54) <2001IC6820>. The cyano-furyl-functionalized persilylated amidine 330, prepared by the reaction of 2,5-dicyanofuran with lithium bistrimethyl-silylamide, was treated with 2 equiv of SeCl2, which was prepared in situ from Se and SeCU- The diselenadiazolylium chloride [30] [Cl] was reduced with triphenylantimony to give the radical 30 in 68% yield from compound 330. 

Analogous products were obtained from the reaction of silylene 85 with silyl lithium compounds, with alkali metal silylamides and alkali metal alkylamides, and sodium methoxide <2000CC1427, 2004JCD3288, 2005JCD2720, 2005CC5112>. In the case of the reaction with metallated silylamides a thermally initiated rearrangement (114 — 115) to give the new silylamide 115 took place (Scheme 11). 

When a deficit of the lithium alkylamide is used, dimeric chloride-bridged silylamides are obtained which are useful synthetic intermediates (Figure 4.10). 

When a deficit of the lithium alkylamide is used, dimeric chloride-bridged silylamides are obtained which are useful synthetic intermediates (Figure 27) they can also be prepared by redistribution reactions between LnCb and [Ln(N(SiMc3)2)3 some bromo- and iodo- analogues have been reported. 

The silanolates are more stable than the silylamides. Using fluorosilyl groups, lithium is coordinated to the fluorine atom. 

Compounds of the type [(Me3Si)2N]3M have been prepared for all of the lanthanide elements except Pm, Tb, Dy, Tm, and Er (4). The synthetic method used in their preparation is nucleophilic substitution with three molar equivalents of lithium -or sodium - bis(trimethylsilyl)amide on the metal trichlorides in tetrahydrofuran. The compounds are rather high melting solids (145-170°C) which can be isolated by crystallization from pentane as long needles or by vacuum sublimation (80-100°C). The binary silylamides are monomeric in refluxing benzene solution, in the gas phase (by mass spectrometry), and in the solid state (by x-ray crystallography, see below). Thus, these compounds are three-coordinate, a unique coordination number for the lanthanide elements. 

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